This invention relates to a method which can recover expensive soluble cyclodextrin from CD formation liquid.
Solutions containing cyclodextrins (CDs) and linear dextrins produced during the reaction of starch with CGTase are called CD formation liquid. CD formation liquids include .alpha.-, .beta.-and .gamma.-CD.
.alpha.-CDs and .gamma.-CD's are water-soluble. Unfortunately, the soluble CDs have not been recovered from CD formation liquid after separating .beta.-CD and have instead been used as food additives with dextrins after being concentrated to syrup.
Since Horikoshi found that a cyclodextrin glycosyltransferase (CGTase) isolated from alkalophilic Bacillus is suitable for producing cyclodextrin (CD), this enzyme has been used to produce .beta.-cyclodextrin (.beta.-CD) in industrial scale. In this method starch is suspended in water solution and hydrolyzed to soluble starch at elevated temperature (80.degree.-85.degree. C.) by CGTase (using CGTase as amylase could reduce the formation of glucose which would inhibit the formation of CD at next process), then the soluble starch is mixed with CGTase again at about 50.degree.-60.degree. C. to obtain CD. The conversion from starch to CD is related to the concentration of substrate (soluble starch) and reaction conditions. 25-32% conversion is obtained at 15% (w/v) of reaction substrate and the conversion is increased to 50% at 5% of substrate residual starch becomes linear dextrins. The contents of the produced CD vary with the type of the CGTase and the reaction conditions, about 4.3%, 77% and 20% of .alpha.-, .beta.- and .gamma.-CD respectively are obtained from 5% of starch by using CGTase from Bacillus sp. No. 38-2. The CD formation liquid is decolorized by active carbon, de-ionized by ion-exchange resin, and concentrated by evaporation. Then .beta.-CD (with lower solubility) is precipitated after being cooled to room temperature. The soluble .alpha.-, .gamma.-CD and a little residual .beta.-CD are not separated and recovered and thus stay with dextrins as syrup liquid or are dried to powder and cheaply used as food filler and additives. The wholesale price of .beta.-CD in the international market is already diminished to U.S. $12/kg due to its easy production. But the international price of soluble CD such as .gamma.-CD is still about U.S. $1200/kg because of production difficulties and it's about 100 times to that of .beta.-CD.